CHRIS UHLMANN, PRESENTER: The agony and the ecstasy of Olympic selection will be played out this week when Australia's swimming superstars take to the pool in Adelaide in trials that will settle the squad for this year's London's Games. In Australia's Olympic glamour sport are some new and exciting names on the cusp of glory and a few former champions struggling to make a comeback, some doing better than others. Here's our Olympics reporter Ben Knight.

GEOFF HEUGILL, FORMER WORLD CHAMPION: I've never been able to simulate that sort of experience. I mean, to walk out in front of a crowd of 10,000 or 15,000 people or to go to an Opening Ceremony of an Olympic Games is something that not everyone every single day gets to have that opportunity to do.

LOUDY WIGGINS, OLYMPIC BRONZE MEDALLIST: It's the best feeling in the world if you've done it well. And it's something that no-one can ever take away from you. I haven't been able to replicate it in any other aspect of my life.

BEN KNIGHT, REPORTER: It's no wonder it's hard to walk away. But why in this Olympic season are so many of the old guard trying to come back?

MICHAEL KLIM, OLYMPIC GOLD MEDALLIST: Well it's in vogue I think at the moment.

BEN KNIGHT: At 34, Michael Klim's career should be well and truly over. But he says the sport's changed.

MICHAEL KLIM: It's great. You know, culturally the sport's always been a young people's sport, and, I think, you know, obviously Geoff Huegill and Libby, they've proven that you can swim into your 30s.

BEN KNIGHT: 10 years ago, Geoff Huegill won three World Championships and an Olympic bronze medal. Huegill famously stacked on weight after he first left the sport. But this comeback is already a success. He's won two Commonwealth gold medals in Delhi.

GEOFF HEUGILL: Yeah, look, it's been tough, you know, like, you have good days and you have bad days. I think me as an individual, sometimes the biggest things that frustrate me is, you know, now that I'm a little bit older and you get a little bit wiser is why I didn't approach training X amount of years ago with that same sort of mindset that I had today.

BEN KNIGHT: Lisa Curry came back twice, both times after having a baby.

LISA CURRY, RETIRED SWIMMER: Going to that first training session, diving in the pool, not having any feel, you're slow, you feel lethargic, you try and sprint and you can't and it's really hard. And it tests you because you sit there and you go, "What am I doing? Do I really want this?"

BEN KNIGHT: The result was Commonwealth gold and an Olympic final in Barcelona.

LISA CURRY: If you wanna get to the top you have to shut everything off; and that's why Ian Thorpe went overseas to train. The downside of that is you think you're doing well, you think you're doing good enough, you think you're on track until you get into a training camp situation with everybody else, and all of a sudden you think, "Oooh, I'm not as fast as I thought I was."

BEN KNIGHT: And that appears to be exactly what's happened. Back in January, Ian Thorpe failed to make the final of the 100 metres freestyle at the Victorian State Championships. He did make the final of the 200, but swam fifth. Some thought he might've been foxing, but since then, Ian Thorpe's times have barely improved. Even back then he was admitting he might not be as on track as he'd hoped.

IAN THORPE, SWIMMER: For London, yes; for trials, not so sure.

BEN KNIGHT: And it all comes down to the trials. Back in 1992, Lisa Curry's comeback almost fell apart in the heats, but she scraped into the final and went on to win and make the team for Barcelona.

LISA CURRY: I would never underestimate Ian Thorpe. I mean, he's strong in the head. He knows - and you know what, he wouldn't have started this if he didn't know that he could finish it off properly. Don't ever underestimate him.

BEN KNIGHT: Libby Trickett has also been struggling to recapture the form that won her three Olympic gold medals. At the moment, she's swimming times that could earn her a place on the relay team. Ian Thorpe is not.

And their comebacks have been making ripples inside the sport because there have been reports that Swimming Australia has been spending massive amounts of money trying to get these old contenders back on the dais instead of developing new talent. Swimming Australia says that's just wrong and that the old swimmers aren't getting an extra cent.

Not all of those trying to come back are battling age. Stephanie Rice is the reigning Olympic champion, but she's been struggling with a shoulder injury for two years and still has a hole in her tendon. Loudy Wiggins is also trying to make a comeback. She missed the Beijing Olympics after injuring herself during the trials. She had dived at three previous Olympic Games. She was the first Australian woman to ever win an individual Olympic diving medal. Suddenly, her career was over in the worst possible way.

LOUDY WIGGINS: I didn't watch any of the 2008 Olympic Games. I was just really unhappy with how well - I thought that I could give more.

BEN KNIGHT: She wants one last shot and she's doing it the hard way as the mother of a two-year-old daughter.

LOUDY WIGGINS: I thought about it and I was like, "OK, this isn't too much of a sacrifice in our lives and it's only a year out and at the end of the day my daughter might actually be proud of me that I followed it."

BEN KNIGHT: You feel that?

LOUDY WIGGINS: I hope so.

BEN KNIGHT: This weekend, hopes will be realised or dashed. Swimmers like Libby Trickett and Ian Thorpe are not just battling the years, but a new batch of emerging superstars who are waiting to take their turn in the spotlight. But the veterans have one advantage: they are already champions and that counts for a lot. But the question remains: how does an athlete know when it is finally all over?

LISA CURRY: I honestly think it's when the enjoyment goes out of it. When it's cold and raining outside and you prefer to stay in bed than to get up, then it's all over.